In recent years, Recommendation Y.1731 is regulated as a maintenance function (OAM (operations, administration, and maintenance) function) in a packet network in the ITU-T (International Telecommunication Union-Telecommunication Standardization Sector). In addition, in order to apply the existing MPLS (Multi Protocol Label Switching) to a carrier network, standardization of MPLS-TP (Multi Protocol Label Switching Transport Profile) that is an expansion of the OAM function is underway by both the IETF and the ITU-T.
In the OAM function of the existing MPLS-TP or the Recommendation Y.1731, an MEP (Maintenance End Point) is defined in each of any two points within a network, and various OAM frames are transmitted and received between these MEPs, thereby monitoring a path or the like between the two points. An LM (Loss Measurement) function is one example of the OAM function.
This LM function is a function of loading the number of transmitted and received frames counted in MEPs of the transmitting and receiving sides on LM frames, mutually exchanging the frames, and thus detecting a frame loss by virtue of a difference between the number of transmitted frames counted in the transmitting-side MEP and the number of received frames counted in the receiving-side MEP.
It is possible to monitor a line quality between the MEPs using the LM function.
Hereinafter, a mechanism for detecting signal degradation by virtue of the LM function that is a related art will be described.
First, an ME (Maintenance Entity) is set between communication devices that try to monitor the line quality. The ME is a unit to be monitored using the OAM function, and may be set for each flow, section, path or the like to be monitored. Both ends of the ME are the MEP described above.
The MEP set in the transmitting-side communication device is referred to as a transmission source MEP, and the MEP set in the communication device of the receiving side is referred to as a destination MEP. In addition, the transmitting-side communication device is referred to as a transmission source node, and the receiving-side communication device is referred to as a destination node.
The transmission source MEP counts the number of OAM frames and the data frames associated with the ME that the transmission source node transmits to the destination node. In addition, the destination MEP counts the number of received OAM frames and the data frames associated with the ME.
The number of frames counted in the MEP is loaded on the OAM frame (CCM (Continuity Check Message) frame) that is periodically transmitted and received as the LM message, and is transmitted from the destination MEP to the transmission source MEP.
The transmission source MEP that has received the frames counted in the destination MEP by means of transmission calculates the number of lost frames by virtue of the equation below.[Number of transmitted frames (current value)−number of transmitted frames (previous value)]−[number of received frames (current value)−number of received frames (previous value)]
In addition, according to the definition of the signal degradation recommended in the Recommendation G.8021, the signal degradation state is regarded as being detected when the number of transmitted frames exceeds a preset threshold (the minimum number of the transmitted frames) and the rate of the lost frames calculated from the number of lost frames exceeds a signal degradation threshold.
That is, when the number of transmitted frames does not exceed the minimum number of transmitted frames, it is not possible to detect the signal degradation state.
By monitoring the line quality in this way, it is possible to issue a signal degradation warning in the line in which the frame loss is occurring and to bypass the failed location, thereby providing a network with high reliability.
In addition, the signal degradation detection (measurement on the line quality) is also defined in the Recommendation G.8021 regulated by the ITU-T.
FIG. 7 is a diagram illustrating data frames transmitted and received between a transmitting-side communication device and a receiving-side communication device.
As shown in the diagram, counting the number of data frames sandwiched between the CCM frames being transmitted and received between the transmitting-side communication device and the receiving-side communication device and measuring the line quality from these counted values are defined in the Recommendation G.8021.
In particular, it is necessary to cause the number of transmitted frames to be greater than a regulated threshold, and it is necessary to transmit and receive the number of frames within a certain period of time in order to measure the signal degradation in the Recommendation G.8021.
In addition, Patent Document 1 describes a connectivity loss detecting method, in which the method detects when an L2 switch to periodically receive an ETH-CCM using a message that becomes the ETH-CCM capable of regulating any of seven kinds of cycle information with 3 bits as a message related to terms of checking the flow rate of the data frames for checking connectivity between management points has not received the ETH-CCM for at least a time duration that is three and a half times longer than the cycle indicated in the cycle information is described in.
In addition, a system for preparing a communication device with a transmission functional unit and a reception functional unit as a device that performs packet switching, causing a statistical information accumulation circuit to compare statistical information of a communication device of a local station with statistical information of the opposite communication device when a data frame reception circuit of the reception functional unit has received statistical information from the opposite communication device, and determining whether or not the data frame is lost in the transmission path is disclosed as a device for exchanging packets in Patent Document 2.
In addition, a system in which measurement nodes regularly or periodically measure traffic states of the routers and transmit measurement packets indicating the communication quality to an external network monitoring device via a dedicated communication path is disclosed in Patent Document 3.